8 Gray areas
This chapter covers
- Historical methods for printing pictures and reproducing photographs using only black ink and white paper
- Computer methods for printing pictures and reproducing photographs using halftoning and dithering
With only black ink and white paper, we can draw both beautiful letters and good line drawings, such as the diagrams of Bézier curves from chapte 2. But what about reproducing photographs? How can we create the intermediate gray tones using only black ink and white paper? In this chapter, we will look at precomputer methods for the reproduction of gray tones and then see how computers can automate the process.
8.1 Simple thresholding
Consider the two images in figure 8.1: a photograph of a camel and a rather higher-resolution picture of a smooth gradient between black and white. We will use thesepictures to compare the different methods of reproduction we discuss. From looking at the page (at least if you are reading this book in physical form rather than on a computer screen), you can see that it is indeed possible, at least when one views the page from a normal reading distance. But how?
Figure 8.1 Our two example images: a photograph and a gradient
